The hydrops ex vacuo mechanism relating Eustachian (ET) dysfunction to otitis media with effusion (OME) descried by Politzer has been more completely developed by investigators at our Center. This mechanism includes four casually related, temporally sequential events: 1) the unabated absorption of middle ear (ME) gases (ET dysfunction); 2) a resultant ME under-pressure ; 3) an increased permeability of the mucosal vasculature, and 4) a transduction of fluid into the ME space. The mechanism is supported by studies of the behavior of other biological gas pockets and is consistent with the predictions of mathematical mod4ls of ME pressure regulation. Recent studies conducted by us showed that hydrops ex vacuo is a valid explanation for the development and persistence of OME under appropriate conditions. However, the mechanism responsible for transducing the biological signal(s) associated with the under-pressure and initiating ME mucosal inflammation is not known, and has not been studied. While osmotic and hydrostatic effects have been implicated as co-factors, biochemical assays document the presence within the provoked effusion of both pro-inflammatory cytokines and other chemicals that may have a transducing function as was demonstrated for OME of other etiologies. Because transduction of this signal initiates the inflammatory process, it represents a potential target for other etiologies. Because transduction of this signal initiates the inflammatory process, it represents a potential target for therapies designed to present mucosal inflammation and OME. Therefore, the primary goal of this project is to define the mechanism for signal transduction including: the nature of the signal (e.g. under-pressure, altered gas composition), the sensory components for signal identification (e.g. osmotic, chemoreceptive, baroreceptive), the early cellular response to the signal (e.g. synthesis of cytokines gap juncture disruption), the role of inflammatory chemicals as secondary signals (e.g. lipid based inflammatory mediators, cytokines) and the physiological response of the mucosa to the primary and secondary signals (e.g. gap juncture formation, altered transmucosal potentials, fluid transduction, inflammatory cell influx). The experiments will involve in vitro (cell culture) and in vivo model systems, and will include histopathological, biochemical (proteins, mRNA, lipids) and physiological outcomes. As in past studies, pharmacological probes will be used to identify the role of specific inflammatory mediators in this process. The biochemical changes that promote healing of the mucosa or cause the purported ME complications of tympanostomy tubes are not yet known, and will be investigated using the above techniques and methods.